Drying metal powders



June 3, 1930. KOEHRING ET AL 1,761,016

DRYING METAL POWDERS Filed Nov. 7, 1927 2 Sheets-Sheet l June 3, 1930.R. P. KOEHRING ET AL 1,761,016

DRYI NC: META T FOWDERS Filed NOV 1927 2 Sheets-Sheet 2 Patented June 3,1930 UNITED STATES PATENT OFFICE ROLAND P. KOEHBINGgOF DAYTON, OHIO, AND CHARLES R..SHOBT, OF DETROIT, MICHI- GAN, ASSIGNORS TO THE MORAINEPRODUCTS COMPANY, OF DAYTON, OHIO, A COR- PORTION OF OHIO DRYING METALPOWDERS Application filed November 7, 1927. Serial No. 231,410.

This invention relates to the drying of owdered material by bringingheated air into contact therewith.

It is the principal object of this invention 1 to devise a novel methodof, and apparatus for, drying any wet powdered material rapidly andefiiciently without injury to the material being dried.

A desirable method of manufacture of 10 powdered copper involvesprecipitation of the copper from a solution of some copper salt, as forinstance copper sulphate. The precipitate, which is an amorphous powder,is washed and after the washing operation as much water as possible isseparated from the wet powder by rotating the wet mass in a centrifugalmachine. After such treatment, however, the mass still contains sometwenty per cent water, and this water must be separated from the powderbefore the latter can be used for various pur oses. It has been founddifiieult to dry t is powder because copper oxidizes very readily andunless the drying operation is carried out very rapidly within certainnarrow temperature limits considerable oxidation of the powder will takeplace.

More specifically, therefore, an ob'ect of the invention is to devise anovel met 0d of dryin wet copper powder in such a way as to red hoe orpractically prevent the formation of cop er oxide during the dryingoperation, and to provide a suitable apparatus for carrying out thismethod.

With these objects in view a feature of the invention resides in amethod of drying wet powdered material which consists in depositing thematerial to be dried in a thin ayer on a orous support and forcingheated air throng the material while on said suport..

p A further feature of the invention resides in the method of drying wetpowdered material which includes the step of depositing the material ina'thin layer on a fabric conveyor and operating the eonveyoreontinuouslyto carry said material through a drying chamber in which heated air isforced through said material while on the conveyor.

An additional feature of the invention resides in the method of dryingwet powdered material as above set forth, said method ineluding the stepof repeatedly subjecting the powdered material to the action of heatedair the temperature of which is varied as the air absorbs moisture, tomaintain the relative humidity of the air substantially constant. Astill further feature of the invention consist in the provision of anapparatus for carrying out the above method which comprises a dryingchamber, a conveyor passing through said chamber, means forcing heatedair through said chamber, and means for depositing material to be driedon said conveyor and removing the material after it is dried.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of one form of the presentinvention are clearly shown.

In the drawings:

Fig. 1 is a sectional view more or less diagrammatic of a drierconstructed in accordance with this invention.

Fig. 2 is a similar view of a modified form of drier.

Referring to Fig. 1 of the drawing the reference numeral 10 indicates ahopper in which the powdered material to be dried is placed. The hopperis provided with a contracted outlet neck 11 from which the material isfed to an endless conveyor belt hereinafter described. The material isejected from the hopper continuously by means of a rotating brush 12suitably supported within the hopper and driven by any suitable means. Ascreen 13 is fixed in the bottom of the hopper by screws 14, in closeproximity to the brush 12. As the brush is rotated it forces thepowdered material through the screen and such material falls'through theoutlet neck 11 to the surface of the belt conveyor. The quantity ofmaterial ejected from the hopper, per unit of time is, of course, de.-

pendent on the speed of rotation of the rush.

An endless belt conveyor 15 receives the material from the hopper. Thisconveyor is made of relatively strong, heavy fabric, such for instanceas the cloth employed in the making of bags for vacuum cl'eaners,'andthe belt is supported on three rollers 16, 17 and 18 mounted in anysuitable manner and rotated by any suitable driving means to operate thebelt continuously. The rollers are driven at such speed relative to thespeed of the brush 12, that the powder ejected from the hopper is spreadin a thin layer on the belt.

The rollers 16 and 17 are arranged in the same horizontal plane, so thatthe belt travels in a horizontal path between such rollers. Between therollers 16 and 17 is a heating chamber indicated in its entirety by thereference numeral 20. This chamber 1s formed by upper and lower hoods 21and 22 respectively, the enlarged lower end of hood 21 being joined tothe enlarged upper end of hood 22 by any suitable means. The chamber 20,has a contracted inlet 23, a contracted outlet 24 and an enlarged middleportion in which a perforated screen 25 is mounted on ledges 26projecting from the wall of the lower hood. The conveyor belt 15 passesthrough the drying chamber 20 immediately above the screen 25, suitableslots 27 and 28 being provided in the hoods 21 and 22 respectively topermit passage of the belt 15 when the hoods are secured together.

The inlet 23 of the drying chamber is connected to any suitable sourceof hot air, while an air pump 29, having intake 30 and outlet 31 issecured to the outlet 24 of the drying chamber. The pump is of ordinarytype and as the construction of the pump is of no importance so far asthe present invention is concerned, it will not be described in detail.

The roller 17 over which the conveyor belt passes is positioned within adischarge chamber 35, formed of upper and lower hoods 36 and 37respectively, the upper hood being closed and the lower being providedwith a contracted discharge neck 38, through which the dried material isdischarged into a receptacle 39. The hoods 36 and 37' are securedtogether in any desirable manner to form the chamber 35, and the latteris positioned immediately adjacent the chamber 20, the walls of thechambers contacting. Slots 40 and 41 are formed in hoods 36 and 37,respectively, to permit passage of the conveyor belt.

Mounted for rotation in chamber 35 with its axis of rotation parallel tothat of roller 17 and positioned close enough to the roller to contactwith the conveyor belt, is a rotating brush 42. This brush is rotated byany suitable means in the same direction as the roller 17, that is bothroller 17 and brush 42 are rotated in a clockwise direction which causesthe brushes at its point of contact with the conveyor belt to travel ina direction 0pposite to the travel of the belt, as indicated by thearrows in Fig. 1. The rotating brush 42 operates to brush the driedpowder from the surface of the conveyor, the powder being dischargedthrough the outlet 38 into the receptacle 39.

In the form of the invention shown in Fig. 2 a single main casing 50 isrovided having a hopper 51 at one end in which the powder to be dried isreceived and a contracted outlet neck 52 at the other end through whichthe dried powder is discharged. The hopper which is at the top of anupstanding portion of the main casing is reduced in size at its lowerend and immediately below the reduced portion the casing is enlarged toreceive a rotating member 53 having projecting blades 54 thereon formingmeasuring troughs between the blades. A rotating brush 55 is providedbelow the dispensing member, above described and immediately below thebrush 55 is a screen 56 which extends entirely across the upstandingportion of the casing previously referred to. The dispensing element 53and the brush 55 are rotated by any suitable mechanism, the element 53operating to deposit successively measured increments of the powder onthe screen 56 as the element rotates. The brush 55 forces this powderthrough the screen to the surface of a belt conveyor hereinafter morefully described.

The belt conveyor 57 is a continuous strip of strong fabric of the typepreviously described. The conveyor passes over two rollers 58 and 59situated in opposite ends of the main casingand rotated by any suitablemechanism to continuously move the conveyor. A plurality of smallrollers 60 mounted in a supporting frame 61 support the upper part ofthe conveyor between the driving rollers 58 and 59 and rollers 62support the lower part of the conveyor between its driving rollers.

The wet powder is deposited on the conveyor adjacent the roller 58 andthe dried powder is discharged from the conveyor as it passes around theroller 59. Between the two rollers that portion of the belt 57comprising the wet powder passes through three adjacent heating chambers65, 66 and 67. A part of the main casing forms the upper portion ofthese chambers while the roller supportin frame 61 constitutes the lowerpart of such chambers. The chamber 67 is provided with an air inlet 68and an outlet 69. A pipe 70 connects the outlet 69 with an inlet 71 tocarry the air from chamber 67 to chamber 66. Air flows from the chamber66 through an outlet 72 and a pipe 73 conveys the air to the inlet 74 inchamber 65. Chamber is provided with an outlet 75 which is connected bya conduit 76 with an air pump 77 having an outlet 78. The inlet 68 andoutlet 78 may commu- 25 more moisture.

Steam pipes 80 are rovided in the drying ation. Copper oxidizes soeasily that it is chambers 65, 66 and 6%, there being one row more orless difficult to dry the powder suc of heating pipes in chamber 67, tworows of 1 pipes inchamber 66 and three rows of pipes in chamber 65. Itwill be obvious that the air passing through chamber 65, through whichthe powder to be dried first passes, is heated to a higher temperaturethan the air in chamber 66 which in turn is kept at a higher temperaturethan the air in chamber 67. The wet powder is therefore subjected to theaction of the heated air repeatedly, and at progressively decreasingtemperatures, that is, the heated air which first passes through thepowder in chamber 65 is'at higher temperature than that which passesthrough such powder in chamber 66 and so on.

The air entering chamber 67 is comparatively dry and absorbs a part ofthe moisture contained in the wet powder. This air then passes tochamber 66 where, being heated to a higher temperature it can absorbmore moisture, and being heated to a still higher tem perature inchamber 65 it can absorb still In other words, by increasing thetemperatureof the air as its humidity is increased, moisture is absorbedfrom the wet powder each time the air passes through the powder.Moreover, by increasing the temperature of the air as themoistureabsorbed by the air is increased, the relative humidity of theair as it passes through the various drying chambers is maintainedrelatively constant. If this air inlet were in chamber 65 and outlet inchamber 67, the arrangement of heating pipes disclosed could bereversed, that is one row of pipes could be placed in chamber 65 andthree rows in chamber 67. However, as it is desired to handle the powdersoon after it leaves the drier, it is desirable that the chamber 67 havethe lowest temperature. For this reason the air from the pump isadmitted first to this chamber, and the smallest number of heating pipesare placed therein. Also there is less tendency to oxidize the materialwhen said materialis a metal if it is first subjected to the action ofdrying air at the maximum temperature of the latter.

In themanufacture of porous metal bear 'ihgs from powdered'metals andother materials, asset forth in the patent to H. M. Williams No.1,642,347 the principal material used is powdered copper. It is 1mortant to produce the copper powder asc eaply as possible and onedesirable method of making 1t is to precipitate such powder from a solutionof copper sulphate or other copper salt and 'to'recover theprecipitate. The. latter is Washed and after the washing operation is vsubjected to the action of a centrifugal machine to eliminate water. Itis impossible to completely d the powder b this method, however, and

r fore the ow er can be used as t must be subjected to a. urther dryingopercessfully without some degree of oxidation. It must be driedquickly, but must not be subjected to too high a degree of heat duringthe drying operation. Applicants have discovered that by passing acurrent of heated air, at a temperature approximately that of theboiling point of water, through a very thin layer of the powder for avery brief interval of time, the powder may be dried-effectivelysubstantially without oxidation.

While the above described apparatus is designed to dry any powderedmaterial whatever, it is particularly suitable to dry copper powder. Toemploy the device disclosed in Fig. 1 for this purpose the air passingthrough chamber 20 should be approximately 100 C. If the form disclosedin Fig. 2 is used for drying copper powder, the air passing throughchamber should be heated to approximately 100 C., the air in chambers 66and 67 being heated to a lesser degree.

While the form of embodiment of the present invention as hereindisclosed, constitutes a preferred form, it is to be understood thatother forms might be adopted, all coming within the scope of the claimswhich follow.

What is claimed is as follows:

1. The method of drying wet copper powder which consists in depositingthe powder in such a thin layer that drying air can pass therethroughsubstantially uniformly over its area on a foraminous support andforcing heated air through said powder at progressively decreasingtemperatures as the moisture evaporates whereby tendency towardoxidation of the copper powder is reduced.

2. The method of drying wet copper powder which consists in depositingthe powder in a relatively thin layer on a foraminous support, firstforcing air heated to approximately C. through said powder for a timeinsufiicient to cause oxidation of the copper, and later progressivelydecreasing the heated air temperature until the copper powder is dry.

3. The method of drying wet copper powder which consists indepositingthe powder in a relatively thin layer on a foraminous supportand repeatedly forcing heated air therethrough at progressivelydecreasing temperatures as the moisture is evaporated.

In testimony whereof we'hereto aflix our signatures.

ROLAND P. KOEHRING. CHARLES R. SHORT.

